A guide handle is provided for working with a brushcutter and this handle is mounted in the region of the center of gravity of the apparatus. In practice, it has been shown that the motor housing equipped with an internal combustion engine moves relative to the longitudinal axis of the guide tube in unfavorable rpm ranges such as idle. This excites torsion vibrations and can, in idle, lead to operating disturbances of the engine including engine standstill. To avoid vibrations, the engine rpm can be set higher but this leads to an unwanted high discharge of toxic substances.
It is an object of the invention to provide a brushcutter which is so improved that a low engine rpm can be adjusted for an operationally reliable running of the engine without limitation caused by vibrations occurring during operation.
The brushcutter of the invention includes: a motor housing; a guide tube having a first end connected to the motor housing and having a second end; a work tool mounted on the second end of the guide tube; an internal combustion engine mounted in the motor housing and having an output; a drive shaft rotatably journalled in the guide tube for connecting the work tool to the output of the engine; the guide tube having an end portion at the first end; the motor housing having a sleeve-shaped collar extending approximately coaxially over the end portion; the sleeve-shaped collar having a free end and the free end being at a distance (a) from the first end of the guide tube; and, means for connecting the collar at the free end to the guide tube so that the collar cannot rotate relative to the guide tube.
The motor housing is provided with a tubular-shaped collar which coaxially engages over the engine end of the guide tube over a defined length. The collar is connected at its free end with the guide tube so that it cannot rotate relative thereto. The connecting location has a constructive spacing of pregiven length to the end of the guide tube facing toward the engine. In this way, the part of the guide tube, which operates as a torsion spring, is shortened between guide tube and engine housing and its inherent frequency is correspondingly increased. The collar itself likewise operates as a torsion spring and, in contrast to the guide tube, can be suitably adapted to the requirements of the rotational vibration problem with respect to cross section, wall thickness and material selection. Especially a configuration of the collar in injection molded plastic provides an adapted spring stiffness. In addition, the plastic provides a high material damping compared to a guide tube made of metal material. Furthermore, the collar can be used as an ergonomically formed carrier holder because of the large cross section thereof compared to the guide tube.
In a region of the anti-rotation connection between the collar and the guide tube, a screw can be provided as a rotation lock. The screw is mounted in the collar and projects into a bore in the guide tube. In this way, a permanent alignment of the guide tube with the parts mounted thereon, such as the guide handle and the tool head, is ensured relative to the housing with minimum complexity.
The free end of the guide tube projecting into the collar is advantageously guided at a location close to the engine via a support having a longitudinal stop and a radial bearing. In this way, a precise alignment of the guide tube with the drive shaft, which is guided therein, relative to the engine is ensured with simple constructive means. At the same time, the bending load of the collar is reduced. Furthermore, the radial bearing, configured in a simple form as a slide bearing, permits a rotation of the engine housing relative to the end of the guide tube facing toward the engine whereby the collar can operate without restriction as a torsion spring and torsion damper. At least one of the surfaces of the guide tube and the slide bearing can be machined to increase the coefficient of friction in a supportive manner whereby friction is generated with a rotational vibration of the engine housing relative to the guide tube and, in this way, the damping of the vibration is increased.
The configuration of the collar in the form of two half shells permits a simple manufacture of the individual parts as well as a rapid assembly. The half shells, in turn, are advantageously configured as one piece with a corresponding component shell of the motor housing. The anti-rotation connection of the collar to the guide tube can be realized in a simple manner by clamping the two shells to each other with threaded fasteners.